Trephination is an early surgery procedure that involves drilling a hole into the skull to treat certain medical conditions. As the image caption explains:

The basic practices and tools have remained largely unchanged for centuries. Among the trephines themselves, with their cylindrical blades, are a large brace to hold the trephines during drilling, two rugines to remove connective tissue from bones, two lenticulars to depress brain material during surgery and a brush to remove fine fragments of bone. The styling of the instruments and their box reflects a long tradition of producing surgical and scientific instruments as finely crafted, gentlemanly possessions.